In 2015, Spaceflight Industries of Seattle WA (simply referred to as 'Spaceflight'), initiated a dramatic new vision: buy a full Falcon 9 and fill it totally with Rideshare spacecraft. There was to be no ‘prime' satellite. There was the potential for ‘co-lead' status for a couple of customers, but otherwise it was an egalitarian mission. This mission was dubbed SSO-A for ‘Sun Synchronous Orbit – A" with "A" standing for the first of a planned series of such launches. 1)

The SSO-A mission takes the concept of a Rideshare – or ‘Multi Manifest Mission' – to a new level. A full Falcon 9 launch vehicle is being dedicated purely to Rideshare spacecraft – there is no ‘Primary' satellite that defines the mission (Figure 1).The approach is analogous to buying a seat on an airplane: everyone is leaving at the same time and going to the same place. No single passenger gets to change the departure time or destination. There are ‘Co-Lead' customer who get limited involvement in determining the launch date, as well as other enhanced services. In the air travel analogy, this would be equivalent to a special first-class ticket that would allow one or two passengers to ask for the departure to be delayed accommodating their schedule. For the SSO-A mission, there is only one commercial customer who has this special Co-Lead status.

In all, there are 51 different customers, representing 14 different countries on the SSO-A mission. There are 16 MicroSats, as well as dozens of CubeSats ranging from 0.25U to 6U.

IPS (Integrated Payload Stack): The SSO-A configuration features an IPS. As shown in Figure 2, the IPS structure consists of multiple structural elements. The two major deployed elements designated the UFF (Upper Free Flyer) and LFF (Lower Free Flyer), as well as various sub-elements as shown in Figure 3.

The ESPA is a standard aluminum ESPA ring with six port with 15" bolt pattern attachment points. This unit is built by Moog CSA Engineering of Mountain View, CA and has flown multiple times.

The CubeStack is an aluminum structure developed for the SSO-A configuration. It houses the UFF avionics, as well as providing port for up to five 6U-size CubeSat dispensers. It was built by LoadPath Engineering.

The Hub is similar to an ESPA Grande but is composite versus aluminum construction. It has six 24" diameter ports. It is built by Airbus Defense and Space (formerly CASA) in Madrid, Spain.

LFF (Lower Free Flyer): The LFF is a hexagonal aluminum structure designed to hold up to twelve 12U – or QuadPack – size CubeSat dispensers. It also includes avionics to autonomously separate all of the CubeSats on the LFF.

MPC (Multi Payload Carrier): The MPC is a load-carrying composite structure. There is a separation mechanism between the lower and upper halves of the MPC. This separation join allows the UFF to be released and to then autonomously deploy the spacecraft attached to it. There are also four platform on the MPC on which four microsats are mounted and deployed. The MPC is an adaption of the ASAP-S multiple payload structure previously built and flown on Soyuz launch vehicles by Arianespace.

The overall mission scenario is shown in Figure 4. Once the UFF and LFF are separated by the launch vehicle, their avionics power up, initialize, and begin separating the spacecraft in a predetermined sequence.

The UFF and LFF both have S-band transmitters for downlinking status to the ground. This data will be received by Spaceflight's ground station network and linked back to the Mission Operations Center (MOC) at Spaceflight's main office in Seattle, WA. In addition, the UFF is utilizing a Globalstar relay to provide a GPS positional solution and telemetry data throughout the mission. This data will also be linked from the Globalstar ground station network back to the MOC.

The telemetry includes verification indicators for each spacecraft separation. Switches on the deployers – separation systems and CubeSat dispensers – are monitored by the UFF and LFF avionics transmitted to ground stations to provide verification of spacecraft separation. Figure 6 shows the preliminary ground track prediction for the first three orbits along with the location of the three Spaceflight ground stations.

After separation from the F9 upper stage, the UFF and LFF autonomously deploy their spacecraft. At the time of the writing, the details of the final separation sequence are being analyzed. A significant challenge in this analysis is to minimize the potential for recontact between objects and creating undesirable space debris, To do this, a complex analysis and simulation is being employed to evaluate the relative dynamics between all of the separated objects. This involves Monte Carlo analyses of multiple parameters that can affect the orbital parameters, such as separation spring variability, mass uncertainty, and free-flyer body rotation rates.

The UFF and LFF do not have active attitude control, so the body rates are minimized by balancing the inertias imparted by the spacecraft separations. The separation sequence attempts to separate spacecraft with similar imparted inertias from opposite sides of the IPS, balancing the imparted body rates.

The general order of the UFF deployment sequence is:

1) Co-Lead Microsats

2) Rideshare Microsats

3) CubeSats

Nominally, separations are timed at 5 minutes apart to allow more time for the spacecraft to accrue separation distance. However, some cases there are separations as short as 15 seconds and the avionics can accommodate simultaneous separations, if needed. All told, the UFF separation sequence lasts until approximately 4 hours and 40 minutes after launch and the LFF separation sequence goes until L+ 5 hours.

The final separation sequence will be defined by the analysis of the spacecraft on the final manifest, running the Monte Carlo conjunction analysis to confirm an adequately low probability of recontact between all of the separated objects. The acceptable threshold was determined via coordination with the FCC as part of getting the frequency approval process for the UFF and LFF.

Making sure the 80+ spacecraft that have been manifested on SSO-A are ready and able to be integrated with the IPS is a substantial effort. To accomplish this as efficiently as possible, Spaceflight has developed a host of standardized processes and methods to streamline the effort.

ICD (Interface Control Document): One of the primary tools used to manage the integration of spacecraft onto launch vehicles in the ICD. For a typical single-to-few spacecraft mission, this can be handled with a typical document processed in MS Word or similar. Reviews and approvals have normally been handled by distribution of discrete review copies of the document, getting back comments and making the changes.

Ultimately, the final document is routed for signature approvals. However, trying to employ this process for the multitude of customers on SSO-A would quickly get unwieldy. Therefore, Spaceflight adopted the online-accessible Jama Software requirements management tool. (https://www.jamasoftware.com/) Spaceflight has also adopted Jama for all of their internal requirements documentation, allowing a direct connection between customer requirements from an ICD to system requirements. An ICD or other requirement document is called a ‘Project' in Jama.

Using Jama, the Mission Management team created ICDs that can be reviewed by each customer via a browser-based interface. Each ICD requirement can be reviewed and approved discretely on a real-time basis. Rather than issuing new releases of a document to circulate for review, progress of the ICD toward completion can be tracked statistically based on how many of the requirements have been reviewed – and ultimately approved – by each participant. Each participant can be designated as either a review or approver. Reviewers can read the document and make comments on each requirement or section of the ICD. Approvers can to the same but have the additional ability to approve or reject each item. Approving is a simple matter of clicking a ‘check mark' box. Alternatively, an ‘X' can be clicked, indicating the item needs more work. All changes are maintained in the Jama database, allowing one to trace the evolution of the ICD.

To avoid reinventing the wheel and maintaining consistency, Spaceflight developed standardized ICD templates within Jama. Because of the differences in complexity and means of the deployment, separated ICD templates were created for MicroSats and CubeSats. When a new customer was signed for the mission, it became a relatively simple matter to copy the template and edit it with spacecraft-specific information. Moreover, Jama has the ability to ‘push' updates to properly linked projects. Therefore, when revisions are identified that apply to all spacecraft on the mission, they can be pushed out for incorporation in all the linked ICD.

Finally, Jama allows verification artifacts to be directly associated with requirements. The definition of the artifact can be included in the same Jama project as the requirements. The actual artifact (i.e. test reports, analyses, etc) documentation can then be linked to the artifact item in the ICD, providing robust documentation of the ICD requirements verifications.

Regulatory Requirements: Complying with regulations established by Government organizations is not exactly rocket science, but can be a major impediment to getting launched. Approvals are required from multiple agencies. These approvals include radio frequency approval from the FCC (Federal Communications Commission) Earth imaging from NOAA (National Oceanic and Atmospheric Administration), and transport to the launch Range from DoT (Department of Transportation). Additionally, the FAA (Federal Aviation Administration) licenses the commercial Falcon 9 launch vehicle via SpaceX.

Each spacecraft organization coordinates their own approvals. However, Spaceflight also needs to gain the appropriate approvals for the stack elements, for transport, as well the UFF and LFF in space since they are free-flying objects. To do this, information from all of the spacecraft is needed.

DoT special permits are typically needed for transporting spacecraft which have lithium ion (Li-Ion) batteries and/or pressure vessels over US streets and highways. Since most spacecraft are now using Li-Ion batteries, these spacecraft also require DoT special permits. Spaceflight is integrating most of these spacecraft at their Auburn, WA integration facility and then subsequently transporting the stack elements to VAFB (Vandenberg Air Force Base). Therefore, they need to get a special permit which encompasses all of the constituent spacecraft, as well as the IPS elements. Evidence of all of the individual spacecraft permits are needed to accomplish this.

Even more vital is FCC licensing. As part of the FCC frequency approval, they also review orbital debris policy compliance. This includes debris mitigation on orbit (recontact & conjunction analyses), reentry within 25 years, and reentry hazards at end of mission. For this, specific spacecraft information is included in the supporting analysis and application. Given the large number of spacecraft on SSO-A, this is not a trivial effort. As mentioned previously, a complex Monte Carlo separation and conjunction analyses was conducted for all of the separating objects on the mission. Similarly, a reentry debris hazard analysis was completed for the UFF and LFF structures and subsystems that remained after spacecraft separation. The results of these analyses, along with other required documentation, were reviewed with and submitted to the FCC for frequency approval.

Getting frequency approvals is critical to facilitate the launch. When SpaceX applies for their FAA license to launch, they submit a list of all spacecraft on the mission. The FAA initiates an interagency review to assure all applicable US Government agencies do not have concerns with any elements of the mission. As part of this review, the FCC provides confirmation that all US-origin spacecraft have the proper licensing. If just one spacecraft on the mission – even a single CubeSat – does not have a license, the FAA will not issue the launch license. Therefore, Spaceflight requires that all spacecraft on the mission – domestic, foreign, or US Government – all provide evidence of proper licensing. If a spacecraft does not provide the necessary proof, they will not be integrated onto the launch vehicle.

Spaceflight also coordinates closely with JSpOC (Joint Space Operations Center) of the United States Strategic Command (USSTRATCOM) which, among other operational duties, monitors objects in Earth orbit. Although it is not a specific regulatory requirement, given the number new objects being delivered to Earth orbit by SSO-A, it was deemed important by Spaceflight to be good space-citizens and assist JSpOC in identifying all of the spacecraft to be launched.

Mission Integration

Integration for the SSO-A mission is occurring at two primary locations: Spaceflight's Integration Facility in Auburn, WA and the SpaceX PPF (Payload Processing Facility) at Vandenberg AFB, CA.

Spaceflight Integration Facility: The development and integration of the mission elements prior to the start of spacecraft integration happens at the Spaceflight Integration Facility. This includes receiving and inspection of all incoming hardware, such as structures, avionics, cable harnessing, spacecraft separations systems, and CubeSat deployers. It also includes the effort to build-up and functionally test the avionics and subsystems.

The Auburn facility was built-out primarily to support the requirements for the integration of SSO-A. Because of the large structures and IPS height fully stacked, a facility was required with a higher ceiling than Spaceflight's prior location in Tukwila, WA could provide. .It includes a larger and more capable certified ISO 8 cleanroom (<100,000 0.5 µm particles/ft3) clean room Figure 7). The new facility incorporates a 3-ton bridge crane to move hardware and integrate dozens of discrete spacecraft The cleanroom has an airlock for moving hardware in and out, a gowning room, and an electrostatic dissipative floor. The air is constantly scrubbed by filters and its conditions are controlled to keep humidity and temperature within required levels. There is also a portable cleanroom tent capable of ISO 7 (<10,000 0.5 µm particles/ft3) for smaller integration work, such as CubeSat-to-dispenser integration. The facility also includes lab bench for testing, allowing testing of new software/firmware on non-flight hardware before testing it on the flight hardware in the cleanroom environment.

IPS Integration and Test: Spaceflight conducts many layers of avionics testing, over the life of the program, from bench-level testing through full system-level, to make sure the UFF and LFF are ready for customer payload integration, flight, and eventual operations. All hardware received from vendors is subject to receiving inspection, to make sure it was built up to specifications. Software is tested incremental, getting more flight-like at each step, until ultimately testing the actual mission scripts that will run during launch. The final tests look at the entire mission duration, from going to internal power on the launch pad, the moment of separation from the launch vehicle, through our on-orbit passes over Spaceflight ground stations. The Mission Simulation Tests can last as long as 16 hours. During these tests data collection and dissemination is simulated, sending the data to the mission management team who will eventually send those data to customers during post-launch operations, so they can locate and communicate with their spacecraft.

Figure 8 shows the flow of how the four major structures come together. The LFF and the upper segment of the UFF are shown in Figure 9 during integration testing. This mechanical process was demonstrated prior to the final integration of each sub-element into flight configuration. The stack up was also previously demonstrated, in the Fall of 2017, in preparation for a modal survey that was successfully completed on the IPS structure.

Spacecraft Integration: After the IPS and all Spaceflight elements are all fully integrated and tested, the Customer spacecraft arrive for integration and preparation for launch. This starts 60 days prior to launch and continues for almost three weeks. With an unprecedented number of customers and spacecraft, careful coordination and scheduling of integration activities is imperative. The Assembly, Integration and Test engineers' preliminary schedule is planned with ½ day fidelity. For the final schedule, integration is being planned to hourly increments. As an added challenge, the timing of customer integration need to factor in which customers are integrating at the same time. Some customer may be competitors, so they would prefer not to reveal any details about their systems to each other. Similarly, there are US Government spacecraft that need to avoid access by foreign nationals. These factors, and more, were considered in creating the detailed integration schedule.

SpaceX statement: On Monday, December 3rd at 10:34 a.m. PST (18:34 GMT), SpaceX successfully launched Spaceflight SSO-A: SmallSat Express to a low Earth orbit from Space Launch Complex 4E (SLC-4E) at Vandenberg Air Force Base, California. Carrying 64 payloads, this mission represented the largest single rideshare mission from a U.S.-based launch vehicle to date. A series of six deployments occurred approximately 13 to 43 minutes after liftoff, after which Spaceflight began to command its own deployment sequences. Spaceflight's deployments are expected to occur over a period of six hours. 5)

This mission also served as the first time SpaceX launched the same booster a third time. Falcon 9's first stage for the Spaceflight SSO-A: SmallSat Express mission previously supported the Bangabandhu Satellite-1 mission in May 2018 and the Merah Putih mission in August 2018. Following stage separation, SpaceX landed Falcon 9's first stage on the "Just Read the Instructions" droneship, which was stationed in the Pacific Ocean.

Orbit: Sun-synchronous circular orbit with an altitude of 575 km, inclination of ~98º, LTDN (Local Time of Descending Node) of 10:30 hours.

This mission enabled 34 organizations from 17 different countries to place spacecraft on orbit. It's also special because it was completely dedicated to smallsats. Spaceflight launched 15 microsatellite and 49 CubeSats from government and commercial entities including universities, startups, and even a middle school. The payloads vary from technology demonstrations and imaging satellites to educational research endeavors.

• CSIM-FD (Compact Spectral Irradiance Monitor-Flight Demonstration), a 6U CubeSat of LASP (Laboratory for Atmospheric and Space Physics) at the University of Boulder, CO, USA. The goal is to measure solar spectral irradiance to understand how solar variability impacts the Earth's climate and to validate climate model sensitivity to spectrally varying solar forcing.

• Eu:CROPIS (Euglena and Combined Regenerative Organic-Food Production in Space), a minisatellite (230 kg) of DLR, Germany. The objective is to study food production in space in support of future long-duration manned space missions (life sciences). The main payloads are two greenhouses, each maintained as a pressurized closed loop system, simulating the environmental conditions of the Moon or of Mars.

• eXCITe (eXperiment for Cellular Integration Technology), a DARPA (Defense Advanced Research Projects Agency) mission to demonstrate the 'satlets' technology. Satlets are a new low-cost, modular satellite architecture that can scale almost infinitely. Satlets are small modules that incorporate multiple essential satellite functions and share data, power and thermal management capabilities. Satlets physically aggregate in different combinations that would provide capabilities to accomplish diverse missions.Built by NovaWurks, eXCITE has a mass of 155 kg. eXCITE also carries the See Me (Space Enabled Effects for Military Engagements), a prototype microsatellite (~22 kg) built by Raytheon for DARPA to obtain on-demand satellite imagery in a timely and persistent manner for pre-mission planning.

• ExseedSat-1, a 1U CubeSat mission by the Indian company Exseed Space. The goal is to provide a multifunction UHF/VHF NBFM (Narrow Band Frequency Modulation) amateur communication satellite.

• FalconSat-6, a minisatellite (181 kg) of the USAFA (U.S. Air Force Academy) and sponsored by AFRL. FalconSat-6 hosts a suite of five payloads to address key AFSPC (Air Force Space Command) needs: SSA (Space Situational Awareness) and the need to mature pervasive technologies such as propulsion, solar arrays, and low power communications.

• Irvine 02, a 1U CubeSat educational mission by the Irvine Public School Foundation, Irvine, CA. The Irvine CubeSat STEM Program (ICSP) is a multi-year endeavor that directly impacts over a hundred students from six high schools and two school districts.

• ITASAT-1 (Instituto Tecnológico de Aeronáutica Satellite), a Brazilian 6U Cubesat (~8kg) built by the Instituto Tecnológico de Aeronáutica (ITA). A former rescoped microsatellite mission.

• JY1-Sat, a 1U CubeSat of Jordan developed by students of various universities. The satellite will carry a UHF/VHF amateur radio.

• KazSTSAT (Kazakh Science and Technology Satellite), a microsatellite (<100 kg) of Ghalam LLP, Astana, Kazakhstan. Developed by SSTL on a SSTL-50 platform including an SSTL EarthMapper payload designed for global commercial wide-area imaging with a resolution of 17.5 m on a swath of 250 km.

• KNACKSAT (KMUTNB Academic Challenge of Knowledge SATellite) of Thailand, a 1U technology demonstration CubeSat, the first entirely Thai-built satellite, developed by students of King Mongkut's University of Technology North Bangkok (KMUTNB). Use of an amateur radio for communication.

• MinXSS-2 (Miniature X-ray Solar Spectrometer-2), a 3U CubeSat(4 kg) of LASP (Laboratory for Atmospheric and Space Physics) at the University of Colorado at Boulder,CO, USA. The objective is to study the energy distribution of solar flare SXR (Soft X-ray) emissions and its impact on the Earth's ITM (Ionosphere, Thermosphere, and Mesosphere) layers.MinXSS-2 is a copy of the MinXSS-1 but with some improvements. — MinXSS-1 was launched on 06 December 2015 onboard of Cygnus CRS-4 to the ISS, were it was deployed into orbit on 16 May 2016. It reentered Earth's atmosphere on 6 May 2017.

• NEXTSat-1, a multi-purpose microsatellite (~100 kg) of Korea designed and developed at SaTReC (Satellite Technology Research Center) of KAIST (Korea Advanced Institute of Science and Technology). The goal is to conduct scientific missions such as star formation and space storm measurements and also technology demonstration in space. Instruments: ISSS (Instrument for the Study of Space Storms) developed at KAIST to detect plasma densities and particle fluxes of 10 MeV energy range near the Earth. NISS (NIR Imaging Spectrometer for Star formation history), developed at KASI (Korean Astronomy and Space Science Institute).

• Orbital Reflector, a 3U CubeSat project (4 kg) of the Nevada Museum of Art and artist Trevor Paylon. The Orbital Reflector is a 30 m sculpture constructed of a lightweight material similar to Mylar. On deployment, the sculpture self-inflates like a balloon. Sunlight reflects onto the sculpture making it visible from Earth with the naked eye — like a slowly moving artificial star as bright as a star in the Big Dipper.

• ORS-7 (Operationally Responsive Space 7), two 6U CubeSats (-7A and -7B) of the USCG (US Coast Guard) in cooperation with DHS (Department of Homeland Security), the ORS (Operationally Responsive Space Office) of DoD, and NOAA. The objective is to detect transmissions from EPIRBs (Emergency Position Indicating Radio Beacons), which are carried on board vessels to broadcast their position if in distress.

• PW-Sat 2 (Politechnika Warszawska Satellite 2), a 2U CubeSat of the Institute of Radioelectronics at the Warsaw University of Technology, Warsaw, Poland. The objective is to demonstrate a deorbitation system - a drag parachute opened behind the satellite - which allows faster removal of satellites from their orbit after it completes its mission.

• RAAF-M1 (Royal Australian Air Force-M1), an Australian 3U CubeSat (~4 kg) designed and built by UNSW (University of New South Wales) for the Australian Defence Force Academy, Royal Australian Air Force. RAAF-M1 is a technology demonstration featuring an AIS receiver, and ADS-B receiver, an SDR (Software Defined Radio).

• RANGE-A and -B (Ranging And Nanosatellite Guidance Experiment), two 1.5 CubeSats of Georgia Tech (Georgia Institute of Technology), Atlanta, GA, USA, flying in a leader-follower formation with the goal of improving the relative and absolute positioning capabilities of nanosatellites.

• ROSE-1, a 6U CubeSat of Phase Four Inc., El Segundo, CA, USA. ROSE-1 is an experimental spacecraft designed to provide an orbital test-bed for the Phase Four RFT (Radio Frequency Thruster), the first plasma propulsion system to fly on a nanosatellite.

• SeaHawk-1, a 3U CubeSats of UNCW (University of North Carolina, Wilmington), NC. The goal is to measure the ocean color in project SOCON (Sustained Ocean Observation from Nanosatellites). SeaHawk is considered a prototype for a larger constellation. The SOCON project is a collaboration between Clyde Space Ltd (spacecraft bus), the University of North Carolina Wilmington, Cloudland Instruments, and NASA/GSFC (Goddard Space Flight Center).

• See Me (Space Enabled Effects for Military Engagements), a prototype microsatellite (~22 kg) built by Raytheon for DARPA to obtain on-demand satellite imagery in a timely and persistent manner for pre-mission planning.

• SkySat-14 and -15. Planet Labs of San Francisco has 13 SkySats in orbit. The commercial EO satellites were built by Terra Bella of Mountain View, CA, which Planet Labs acquired from Google last year. At the time of the purchase, there were 7 SkySats in orbit. On 31 October 2017, Planet launched an additional six on a Minotaur-C rocket. The 100 kg SkySats are capable of sub-meter resolution – making them the most powerful in the constellation. Customers can request to have these high-resolution satellites target their locations of interest.

• SNUGLITE, a 2U CubeSat designed by the SNU (Seoul National University) for technology demonstrations and amateur radio communication.

• SpaceBEE, four picosatellites of Swarm Technologies (a US start-up), built to the 0.25U form factor to make up a 1U CubeSat.

• STPSat-5 is a science technology minisatellite of the US DoD STP (Space Test Program), managed by the SMC of the USAF. STPSat-5 will carry a total of five technological or scientific payloads to LEO (Low Earth Orbit) in order to further the DoD's understanding of the space environment. The satellite was built by SNC (Sierra Nevada Corporation) on the modular SN-50 bus with a payload capacity of 50-100 kg and compatible with ESPA-class secondary launch adaptors.

• THEA, a 3U CubeSat built by SpaceQuest, Ltd. of Fairfax, VA to demonstrate a spectrum survey payload developed by Aurora Insight, Washington DC. The objective is to qualify Aurora's payload, consisting of a proprietary spectrometer and components, and demonstrate the generation of relevant measurements of the spectral environment (UHF, VHF, S-band). The results of the experiment will inform future development of advanced instrumentation by Aurora and component development by SpaceQuest.

• VESTA is a 3U CubeSat developed at SSTL in Guildford, UK. VESTA is a technology demonstration mission that will test a new two-way VHF Data Exchange System (VDES) payload for the exactEarth advanced maritime satellite constellation. Honeywell Aerospace is providing the payload. VESTA is a flagship project of the National Space Technology Program, funded by the UK Space Agency and managed by the Center for EO Instrumentation and Space Technology (CEOI-ST).

• VisionCube-1, a 2U CubeSat designed by the Korea Aerospace University (KAU) to perform research on Transient Luminous Events in the upper atmosphere. The image processing payload consists of a multi-anode photon multiplier tube(MaPMT), a camera, and a real-time image processing engine built by using SoC (System-on-Chip) FPGA technologies.

Spaceflight has contracted with 64 spacecraft from 34 different organizations for the mission to a Sun-Synchronous Low Earth Orbit. It includes 15 microsatellites and 49 CubeSats from both commercial and government entities, of which more than 25 are from international organizations from 17 countries, including United States, Australia, Italy, Netherlands, Finland, South Korea, Spain, Switzerland, UK, Germany, Jordan, Kazakhstan, Thailand, Poland, Canada, Brazil, and India. 6)

Figure 14: This infographic released by Spaceflight illustrates the types of payloads booked on the SSO-A mission (image crdit: Spaceflight)

Statement from the Mission Manager of Spaceflight

Most will never know all that is necessary to plan a launch, and then add to that the challenge of managing and being responsible for the launch of 64 satellites, a record breaking event to be sure, but that's exactly what Spaceflight did. 7)

Spaceflight, the leading rideshare and mission management provider, today announced the success of its SSO-A: SmallSat Express mission, the largest single rideshare mission from a U.S.-based launch vehicle to date. The company successfully launched 64 spacecraft to sun-synchronous low Earth orbit via a SpaceX Falcon 9 that launched today from Vandenberg Air Force Base.

"This was an incredibly complex mission, and I'm extremely proud of what our talented team at Spaceflight has achieved," said Curt Blake, president of Spaceflight. "SSO-A is a major milestone for Spaceflight and the industry. We've always been committed to making space more accessible through rideshare. This mission enabled 34 organizations from 17 different countries to place spacecraft on orbit. It's also special because it was completely dedicated to smallsats."

Figure 15: Photo of the happy Spaceflight team after the launch of the SSO-A mission (image credit: Spaceflight)

Spaceflight launched 15 MicroSats and 49 CubeSats from government and commercial entities including universities, startups, and even a middle school. The payloads vary from technology demonstrations and imaging satellites to educational research endeavors.

One research payload includes the University of North Carolina Wilmington's CubeSat, SeaHawk-1 carrying the HawkEye Ocean Color Imager. UNCW has been funded by the Gordon and Betty Moore Foundation, and NASA serves in an advisory capacity to ensure the maximum scientific utility of the science data. NASA's Science Mission Directorate and UNCW have created a partnership to expand accessibility to the data.

"We are thrilled to have SeaHawk-1 on orbit and to be part of such a historic launch superbly executed by Spaceflight," said Professor John Morrison, SeaHawk's co-project manager and lead principal investigator. "SeaHawk will make ocean observations at significantly higher spatial resolution and at much lower costs than standard satellite systems. Since the data collected will be publicly available, our hope is that it will benefit not only researchers, but policymakers and others to make informed decisions when addressing issues related to the environment."

To accommodate the large number of payloads, Spaceflight built an integrated payload stack that was nearly 20 feet tall. Once the launch vehicle reached orbit, the upper and lower free flyers separated from the vehicle. The free flyers then successfully deployed all spacecraft, dispensing one payload every five minutes over five hours.

"This launch was an impressive undertaking and an important milestone for the smallsat industry as well as for many of the organizations involved," said Payam Banazadeh, founder and CEO of Capella Space Corporation. "Capella's first satellite is now on orbit and we are one step closer to our goal of providing timely, reliable, and frequent information using Synthetic Aperture Radar technology."

With the success of SSO-A, Spaceflight has now launched more than 210 satellites since its founding in 2011. In addition, the company is contracted to launch nearly 100 satellites in 2019. Among the upcoming launches is Spaceflight's next dedicated rideshare mission, which will occur in 2019 on a Rocket Lab Electron.

Mission status - a hindsight view

August 2019: Spaceflight's record-setting SSO-A mission successfully launched 64 customer spacecraft into orbit onboard a Falcon 9 launch vehicle on 3 December 2018. SSO-A is a unique mission because it was a dedicated rideshare mission without a primary spacecraft. All 64 cubesats and microsats shared a ride together to orbit. The diverse number of organizations represented on this mission were all at different levels of maturity for their spacecraft, and this resulted in numerous mission design revisions to SSO-A as the customer manifest changed significantly over the course of the mission. Spaceflight created a flexible hardware architecture, analytical tools to rapidly update mission analyses, strict configuration change control, and quality processes to facilitate these changes and ensure mission success. 8)

SSO-A Smallsat Express: The Beginning

Customer Demand: Spaceflight launched its first customer spacecraft on 19 April 2013. On the surface, this humble beginning was not particularly unique, as satellite have launched as secondary payloads to a prime satellite before. But this time the ride to space was provided by a commercial company that does not build the rocket, does not build the separation system, and does not build the satellite. It was a company that is truly independent of the hardware that sends spacecraft to orbit, and therefor able to leverage all the capabilities and capacities in the commercial market to bring cost-effective launch services to the underserved small satellite launch market. Shortly after this first cubesat launch, customer demand for launch services grew significantly, to include microsats as well as cubesats. The demand was greater than the existing launch capacity, so an audacious plan gradually took shape; to purchase an entire rocket and fill it with small satellites and make a dedicated rideshare mission. Since the majority of customers needed a sun synchronous orbit, and this was the first dedicated rideshare mission, the mission named itself: SSO-A.

Business Case: Space companies love to do cool things. Space companies that stay in business do cool things only if the business case closes. The same philosophy applies to rideshare. A dedicated rideshare mission sounded really cool, but did the business case close? The short answer is yes, but the longer answer involves the flexible mission architecture that enabled Spaceflight to make numerous changes to the manifest as customers dropped off and new customers were added onto the mission. This paper will describe the architecture that made SSO-A possible, the processes that Spaceflight implemented to ensure its success, and the flexible launch campaign plan that brought the plan to fruition (see Figure 2).

Original Concept: The original mission architecture for SSO-A was simple; use several structures to launch about 15-20 microsatellites and some cubesats to orbit. Several of the Spaceflight customers were microsatellites that were larger than the Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA) standard size, resulting in a mission physical architecture as follows:

• Multi Payload Carrier (MPC) manufactured by Airbus Defense and Space. A carbon composite structure that allow four microsats to be integrated parallel to the rocket thrust axis, with a large area inside for a fifth large microsat. The canister is released by a clampband.

Figure 16: MPC. Note that the microsat that was originally inside the MPC was replaced by a structure called the Lower Free-Flyer that will be discussed later (image credit: Spaceflight)

• HUB manufactured by Airbus Defense and Space. A composite ring structure that has six 24" circular microsat interfaces.

The mission concept started with the launch vehicle commanding the separation of the MPC clampband, releasing the upper free-flying segment with a Spaceflight-provided avionics system to command the subsequent separation events. The launch vehicle would then command the separation of the five spacecraft on the MPC, followed by a deorbit maneuver.

This architecture was driven primarily by three factors. First was the quantity of microsats that were anticipated to fly on the mission which led to the two rings with six ports each. Second was the requirement from several customers to integrate vertically onto the stack which led to the selection of the MPC with its four microsatellite platforms. Third was the presence of two large microsat (350-600 kg). These microsats were the two biggest customers on the mission, and they needed a specific volume in excess of the standard offering. The heavier was located inside the MPC and the other on top of the ESPA ring. Ironically, neither of these mission-defining customer would ultimately fly on SSO-A.

Figure 17: Upper Free-Flyer Configuration. Note that the MPC forward canister is bolted to the HUB above, and connected via a clampband separation system to the MPC lower canister (image credit: Spaceflight)

Mission architecture

Flexible Architecture: The key to rideshare is flexibility, and there are three components to flexibility in the space launch industry. The first element are multi-purpose structures and avionics. Flexibility allows Spaceflight to change one customer for another with little or no impact to the overall mission-specific analyses, mission profile, or hardware. Changing a customer no longer triggers complete mission redesign as long as the critical parameters stay within the design envelope. Changing a customer is more like changing an airline ticket than changing the airplane.

Structures: The basic mission architecture was designed to be flexible from the start with six 15" ports, six 24" ports, and four platforms that could accommodate 11" to 24" interfaces. Spaceflight's engineering team added some unique port adapters to accommodate a much wider variety of interfaces. Some of these interfaces include:

• Dual Port Adapter (DPA). Allows two microsats to be mounted on a single 24" port.

Figure 18: Finite element model of a DPA (image credit: Spaceflight)

• X-Pod Adapter. Allows up to three X-POD DELTA dispensers a dispenser (built by UTIAS Space Flight Laboratory; not affiliated with Spaceflight, Inc) to be mounted on a 24" port.

• QuadPack Plate (QPP). Allows up to seven QuadPack dispensers to be mounted to a single 24" port.

• Cubesat Dispenser Adapter Plate (CDAP). Allows up to four cubesat dispensers to be mounted to a single 15" port.

• CubeStack. A spacer between rings that allows up to six cubesat dispensers. Designed and built by LoadPath.

Figure 19: A CDAP with four 12U CSDs. Note the different bolt patterns to allow different dispenser types to interface with this structure (image credit: Spaceflight)

• Lower Free-Flyer. A structure that can carry up to twelve cubesat dispensers and avionics. This structure replaced the microsat customer inside of the MPC, and caused Spaceflight to rename the original free-flyer the Upper Free-Flyer. Designed and built by LoadPath.

• Cube Cone (not flown). A structure that interfaces from an ESPA standard 1575 mm diameter to a reduced circular interface (38") with up to six cubesat dispensers. Designed and built by LoadPath.

Figure 20: Lower Free-Flyer in flight configuration. Note the two different types of dispensers, the mass model (right) that replaced an unpopulated dispenser, and the DragSail (silver object to the lower right). The avionics system is on top (image credit: Spaceflight)

As the mission developed, several other structures were added. Most notably were the SoftRide Isolation System consisting of sixty titanium spring-dampers built by Moog CSA Engineering, and the DragSail de-orbit devices consisting of a 16 m2 aluminum sail built by Surrey Space Center. The isolation system was added by a customer with a microsat that was sensitive to high frequency vibrations. The DragSail was added by Spaceflight to ensure that the Upper and Lower Free-Flyers would deorbit within 25 years in the event that their avionics arrived dead on orbit and did not deploy any customer spacecraft.

Figure 21: From top to bottom: Cube Cone, ESPA, SoftRide Isolation System, and the CubeStack. The Cube Cone was later removed from the mission when the microsat on top was not ready (image credit: Spaceflight)

Avionics: The avionics system for SSO-A was designed to be a simple sequencer with a master controller that can supply any of the five types of separation signals on the mission, with expandable signal cards to provide primary and redundant signals to each separation system. The sequencer needed to be reprogrammable, even a few weeks before launch, to create a separation sequence based on the final configuration. The sequencer only had to last through the six-hour deployment sequence and telemetry download, so there were no requirements for radiation hardening or other environmental factors for long-duration space exposure. A total of six systems were procured, two sets for each free-flyer, with each set consisting of an engineering test unit, a flight unit, and a backup flight unit. Ecliptic Enterprises Corporation was selected to build the avionics system, modeled after a similar space-qualified system, after a competitive source selection.

The avionics system was also required to provide telemetry to confirm separation of all spacecraft. To do this, a Space Dynamics Laboratory Cadet UHF radio was used to transmit telemetry to the three Spaceflight Networks ground stations. The simple telemetry packets would provide telemetry confirming the separation signals and separation confirmation. This information was originally planned to be beaconed every minute until the batteries died; about seventeen hours. However, due to government weather spacecraft that use the same UHF frequencies, the mission CONOP was changed to beacon every two minutes only when over the three ground stations, and to shut off after the last pass post-deployment (after about six hours on orbit). This reduced the transmission time by 97%, allowing the government to concur with the frequency use.

There was no uplink capability to the SSO-A avionics. There was no requirement to provide an uplink, and there was no need for any ground commands since the sequencer was an automatic system triggered by free-flyer separation. Furthermore, a ground commanded system would greatly increase the complexity of the avionics and may have led to expensive downstream requirements such as cyber security, encryption, additional antennas or an attitude control system for what was essentially a six-hour mission. The decision to not have an uplink caused significant consternation during the FCC licensing process, to the point that an uplink will be used on future missions with free-flyers, even if the purpose is only to be able to turn off the transmitters in the event of signal interference with other satellite operators.

Two video cameras were part of the original avionics specification, but this element was removed once it became apparent that only a few pictures could be downloaded over UHF given the few ground station passes before the batteries were exhausted. The pictures would have made great promotional material, but they did not directly tie to mission success.

Having the Right Attitude: The SSO-A mission ended up with two free flying spacecraft dispensers, imaginatively named the Upper and Lower Free-Flyer. Each Free-Flyer had their own avionics and battery power, but neither had propulsion nor attitude control. None of our customers needed a particular deployment orientation, nor should they expect one as a rideshare customer.

Spaceflight's other concern regarding attitude control was the probability of recontact between customers after deployment. Early mission analyses by Spaceflight indicated that the two key factors to reduce the probability of recontact are the relative separation orientation and separation timing. The attitude of the free-fliers at the start of spacecraft deployment was not necessary as long as all of the subsequent deployments were correctly modeled. To do this, Spaceflight created a six degree-of-freedom recontact analysis tool that models the relative distance of every spacecraft given the separation time, spacecraft mass, separation velocity, tip off rates, and the cumulative body rates of the Free-Fliers themselves. This tool allowed engineers to quickly assess the merits of multiple separation sequences and ultimately develop rules for the ever-changing separation sequence (due to changes to customer manifest) so that the probability of recontact could be minimized. Spaceflight's ability to perform the high-fidelity separation analysis of free flying deployers eliminated the need for any attitude control system, and the cost savings were passed down to the customers.

Figure 23: Graph showing the increase of relative distance between customer spacecraft over time (image credit:Spaceflight)

Mission Planning

Flexible physical architecture is only the first of three factors that enabled flexible launch and resulted in the success of the SSO-A mission. Mission planning is the second major element. Although one of the goals of flexible launch is to reduce the need for multiple mission analyses by the launch vehicle provider, Spaceflight had to run most mission analyses dozens of times to ensure that configuration changes stayed within the bounds expected by the launch vehicle. The critical elements that allowed Spaceflight to do this are discussed below.

Customer Requirements and Verification: Good mission design starts with good mission requirements. Spaceflight created two standard Interface Control Document (ICD) templates that covered all SSO-A customers; one for cubesats and one for microsats. Each ICD followed a standard format, with limited tailoring. All cubesats had the same environmental test requirements no matter where they were on the structure. Microsatellites also had similar requirements, although their specific environmental load test requirements did depend on where they were on the physical architecture. Spaceflight utilized digital tools such as Jama Connect to perform revision control of the ICDs as well as track the verification status of each requirements. Other software tools like JIRA were used to allow the Spaceflight Engineers and Mission Managers to collaborate on customer verification artifacts. These tools allowed everyone in Spaceflight to find the current "source of truth" about customer design, track the status of customer verification, and gave the Engineering team the data they needed to perform mission level analyses, which were then documented in shared internal webpages using Confluence software.

Configuration Control: One of the key tools used to track the configuration of the SSO-A mission was a Visio document called the SSO-A Physical Architecture. On a single page, the following information was documented using text, symbols, and formatting:

• Structural hardware and adapters

• Spacecraft name at each port

• Deployment system at each port

• For CubeSats, door assignments and location within the door for sub-3U spacecraft.

This document was under configuration control and displayed on a shared Confluence web page for the entire Spaceflight team to see. Underneath the Physical Architecture was a change log. Any time a customer change occurred, it was posted in the change log as a proposed change. Once enough proposed changes were posted to constitute a significant change (meaning a change to deployment system or requiring a new analysis to be performed), Spaceflight held a configuration change board that included Mission Managers (customer status), Engineering (hardware and analysis), Regulatory (licensing and export), and Sales (contracts and new customers). Each proposed change was summarized, and impacts to the entire mission, not just engineering, were discussed.

Often, a "simple" swap of spacecraft would lead to multiple second order effects. For example, microsat changes often required a rebalancing of the stack, updated mass properties, new thermal models, changes to separation system harnessing, and new umbilical harnessing. Even cubesat swaps needed a close look due to dispenser specific designs, mass differences, and deployables.

Once all factors were discussed, each proposed change was accepted or rejected, and a new Physical Architecture drawing was routed for review and approval by the mission leads. For SSO-A, there were 196 dispositioned changes, and revision W of the Physical Architecture is what flew (only 22 revisions published- "Rev O" was skipped because it could be confused with "zero").

Figure 24: Example of the SSO-A Physical Architecture document which tracked the location of all customers and deployers on the mission (image credit: Spaceflight)

Mission Analyses: To have a successful mission, all mission analyses must be complete and results reviewed and approved. Mass properties, tip off, thermal, venting, coupled loads, power budget, link margin, separation, loads, orbit lifetime, re-entry debris hazard, vibration, etc.... and these analyses must be set up in a way so they can be re-run quickly and efficiently. For SSO-A, there were 88 versions of the SSO-A coupled loads analysis (CLA) model. Now, it is impractical to redo an analysis for every change, not to mention the mental health of the engineering team if they had to redo all analyses for every one of the 196 changes on SSO-A. To bound the problem of an ever-changing manifest, the engineering leads would look at each change to determine which ones need to be redone, and when. Most analyses were re-run before a major design review, but some did not need to be updated. For example, the thermal analysis was not re-run when customers with no thermal requirements were moved between thermally-isolated areas.

Figure 25: One of the finite element models used to run the couple loads analysis (image credit: Spaceflight)

Mission Test and Simulation: There is a reason why they say "test as you fly" in the space industry; because you will not have a chance to fix it after launch. But the conundrum facing astronautical engineers is that there are few practical ways to test everything exactly as if it was in space. To address this, Spaceflight ensured that all deployment system hardware and electrical harnesses were tested according to specification. This includes thermal vacuum cycling and reliability testing. Once the hardware was delivered, receiving inspections were performed to ensure no damage occurred during transit and all specifications were met.

It was impractical to perform system-level testing with all of the flight deployers for various reasons, such as deployer cycle ratings and the sheer quantity of systems. So Spaceflight designed and procured sixty Separation System Simulators (SSS) that could be programed to simulate any dispenser, and provide separation signal measurements via ethernet to a test console. These SSSs were connected to the flight harnesses and flight structure for system-level testing. Spaceflight executed eight mission simulation tests and numerous supporting tests in this configuration with the SSO-A avionics system and harnessing. These tests increased in complexity until the full mission profile was tested, from last charge before launch until the near exhaustion of the rechargeable batteries.

Spaceflight encountered several anomalies and non-conformances during system level testing. Each time this happened, the appropriate action was performed per Spaceflight's quality process, whether a failure review board, non-conformance report, or written product deviation. No issues were wished away; they were ruthlessly examined, documented, and resolved. Throughout the mission there were 16 Failure Review Boards, 75 Non-Conformance Reports, 42 Product Deviations, 57 Requests for Waivers, 62 recorded mission-level risks .... and one successful launch! The success of SSO-A reflects a disciplined engineering team that fully embraced quality processes. The quality process and mission simulation tests gave the Spaceflight team confidence in the full system before shipping to the launch site.

The final component of SSO-A was the successful execution of the mission from the arrival of the first customer, to the last confirmation of separation on orbit. The SSO-A launch campaign was planned to be 60 days from start to finish. This would allow cubesats that only had 90 days of battery charge to integrate with several weeks of margin in the event of a launch delay. The first twenty days of integration occurred at the Spaceflight Integration Facility (SIF) in Auburn, Washington, for all cubesats and four microsats. Integration was followed by five days of packing by Spaceflight and three days of trucking to Vandenberg Air Force Base (VAFB), California. The first 22 days at VAFB encompassed the processing, fueling, and integration of the final eleven microsats and the assembly of the SSO-A stack onto the Falcon 9 Payload Attach Fitting (PAF). At L-10 days, Spaceflight turned over the completed SSO-A stack to SpaceX for encapsulation and integration onto the Falcon 9 rocket.

Flexible Execution: Inevitably, something will not go as planned when you have 35 organizations trying to integrate 64 spacecraft in fifty days. So Spaceflight planned the integration schedule with that in mind. The launch campaign began at the Spaceflight Integration Facility with cubesats. The cubesat integration used two workstations, each focused on filling one dispenser at a time. There were usually two customers, one at each station, in the morning, and two customers in the afternoon to load their cubesats. This plan did deviate to account for sub-3U cubesats that were required to all integrate simultaneously, and for customers with multiple cubesats or pre-loaded cubesats in customer-provided dispensers. This sustainable flow deliberately had several vacancies in the schedule for the inevitable issues that cropped up. Seven spacecraft did not show up and missed the mission. Five customers had to reschedule for various reasons, but only by a few days. One spacecraft was lost for a week at a shipping hub in Memphis (note: pay the extra money for tracking services). And one customer completed integration as scheduled, only to realize that they wired their solar panels incorrectly two days later while reviewing their closeout photography (they were able to return, deintegrate, repair their spacecraft, and reintegrate). Even though Spaceflight could not anticipate these specific issues, the flexible schedule allowed all of our customers who showed up to integrate their spacecraft with enough time for Spaceflight to pack everything up and ship to Vandenberg.

Vandenberg integration was much more challenging because it involved ten customers (five US and 5 foreign) to be integrating at the same time in the same location on a U.S. Government military base. There were 29 Spaceflight employees and 235 customer employees who submitted badging information to participate in the launch campaign. Some of these customers are direct commercial competitors to each other, and some customers represented sensitive U.S. Government spacecraft. Spaceflight gave each customer a 10' x 16' (~3 x 5 m) integration area that was visually and physically screened off from each other, and foreign and U.S. workers wore different colored hair nets on the Payload Processing Facility (PPF) floor. Each customer was limited to a maximum of five people in the clean room at a time. Spaceflight worked one 12-hour shift per day, with all hazardous operations occurring during a night shift. Spaceflight set up the master schedule based on inputs from each customer, with the output having one spacecraft complete integration onto the SSO-A structure per day. Although there were a fair share of issues encountered by spacecraft teams, all teams were able to meet their integration times and there were no major changes to the SSO-A processing schedule while at VAFB. This achievement was a direct result of having a clear understanding of each customer's processing requirements, establishing a reasonable integration schedule, communicating that schedule and integration facility constraints to each customer early, and having clear lines of communication throughout the launch campaign.

Legal and Regulatory: The legal and regulatory requirements to execute rideshare missions are massive. Not only did Spaceflight need to obtain licensing for SSO-A, but also validated and verified the licensing of each customer on the mission. Several customers were from countries that do not have an agency that deals with licensing spacecraft, which made the verification of licensing rather challenging.

One customer was unable to obtain the appropriate license in the timeline required and therefore the spacecraft was sealed inside of their dispenser. Several days later, the license was granted, but too late to unseal the dispenser or provide a technical solution to allow for deployment of the spacecraft. Although the specifics of this incident are beyond the scope of this paper, this was an unfortunate example of an uncertain regulatory requirements for a unique customer, and the consequences of not obtaining licensing.

Results

So how did SSO-A really go? SSO-A launched 64 spacecraft on two free flyers into the desired orbit. One spacecraft was sealed into their dispenser due to delayed licensing and did not deploy. All spacecraft that were supposed to deploy were deployed. Of the 63 deployed spacecraft, 59 were successfully contacted by their owners, a 94% success rate.

In addition to the customer success rate, the Combined Space Operations Center (CSpOC) did not observe any recontact events between spacecraft on the mission. The DragSails for both free flyers deployed as expected based on observations taken by the Surrey Space Center.

Figure 15 is a photo of the Spaceflight team during the SSO-A launch campaign.

Challenges

The Spaceflight team overcame many challenges and established hardware, processes, and teams that will improve future rideshare missions. The small satellite community is still growing, and it is challenging to hold together a mission of this size without a fully mature customer base. Customer readiness (technical, regulatory, and financial) and experience with launching spacecraft spans a very broad spectrum. This introduces a variable of unpredictability in executing multi-manifest missions, which may translate to higher launch costs as launch providers budget for that risk. Spaceflight's approach, a mix of large and small flexible rideshare missions on different launch vehicles, is an answer to support the diverse small satellite market during this period of rapid growth.

Launch capacity is an issue that has been improving recently, albeit only to keep pace with the increasing number of spacecraft and still with poor schedule reliability. One of the reasons why SSO-A was created was due to an abundance of small satellite customers, but a lack of affordable launch opportunities.

Spaceflight continues to expand launch opportunities by making early strategic commitments to emerging small and medium launch vehicle providers, and creating new multi-manifest rideshare missions in partnership with our existing global portfolio of launch providers. More access to space is a win for everyone.

Regulatory issues are another challenge as the number of spacecraft in orbit increase. Particular to SSO-A is the need to identify all of the spacecraft on the mission. As of 10 June 2019, there are 12 spacecraft (18%) from SSO-A who have not self-reported their spacecraft to the CSpOC. This highlights a challenge to the small space community going forward, because accurate and timely identification of spacecraft is needed to perform space traffic management functions.

Epilogue: Future of Rideshare

SSO-A was a very unique mission designed to serve the growing small satellite market when there were few choices for affordable access to space. Spaceflight forecasts rideshare customer demand for more diverse launch opportunities, across a network of rockets, with flexible architectures and contracting terms. Combining over thirty organizations on one large mission may be part of meeting that market need, but it cannot sustain it alone. At least a dozen missions a year with up to fifteen customers at a time gives our existing smallsat industry the critical combination of both capacity and frequency to meet their mission needs and supports the growing launch vehicle industry as well. In whatever form they take, rideshare opportunities will remain essential to enable the next generation of new smallsat entrants and growth, just as it did with SSO-A.

Figure 28: The Spaceflight SSO-A mission patch. Each nation that had a payload on SSO-A is represented by their national flag. The spacecraft shown on the patch are not the actual spacecraft that flew in order to maintain customer spacecraft confidentiality (image credit: Spaceflight)

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net)